I. Field of the Invention
The invention relates to a method and apparatus for conducting wireline operations in oil and gas wells under blowout conditions, and includes a releasable annular wireline blowout preventer.
II. Description of the Prior Art
It is frequently necessary to periodically introduce various cable, or wireline, suspended well tools or instruments into open hole or producing oil or gas wells. Where a well is producing or is an open hole well and contains well fluids such as drilling mud at high pressures, the upper end of the well casing is closed by suitable valving apparatus and special well-servicing equipment must be provided to safely introduce and remove such wireline tools or instruments.
In performing wireline operations for wells under pressure, it is required that the well pressure be controlled during such operations. It must be possible to: lower the wireline suspended tool into the well; perform the conventional wireline operations, such as well logging or perforating operations; and recover the wireline suspended tool, while the well remains sealed. Since all wireline operations involve a moving wireline, or cable, a seal must be provided to prevent well fluid or gas from escaping from the well, while simultaneously allowing free movement of the cable. Furthermore, although an uncased well is normally held under pressure control by drilling mud present in the well, occasionally the pressure forces become unbalanced and the well blows out. Because of such potential emergency situations caused by excessive pressure buildup, or blowout conditions within the well, it is necessary to provide the well with pressure control equipment to quickly allow the well to be sealed when such blowout conditions are encountered and thereafter safely recover the wireline suspended tool.
Accordingly, conventional oil and gas wells which include a main cut-off valve on the wellhead have been provided with a blowout preventer temporarily connected to the cut-off valve on the wellhead. To such blowout preventer, a riser comprising one or more lengths of pressure-control pipe is installed. The riser is sealed at its upper end by a stuffing box, or line wiper, to provide a pressure seal around the wireline at the point where the wireline exits from the riser.
In this manner, when the main wellhead cut-off valve is closed, the wireline suspended tool can be safely inserted into the riser. The wireline is then passed through the stuffing box which is then sealed about the wireline. After the main cut-off valve is opened, the wireline suspended tool is lowered through the open blowout preventer and on into the well. Representative examples of such devices and methods of operation may be found in U.S. Pat. Nos. 3,416,767, issued to L. Blagg and 3,887,158, issued to J. Polk.
In each of the foregoing patents, pressure control at the wellhead during the performance of wireline operations is provided by: a blowout preventer, or wireline valve, provided above the main cut-off valve; a long length of riser attached to the blowout preventer; and a stuffing box provided at the upper end of the riser.
Although such devices and methods of operation provide a means of removing wireline tools from an oil well under blowout conditions, without compromising established safety practices, such devices and method of operation require a great amount of equipment. This equipment must always be installed at the wellhead prior to the time when wireline operations are commenced in order to assure that the well may be controlled during emergency blowout conditions. Most of the time, the installation of such equipment is unnecessary especially in open-hole wells where most wells remain under control and blowout conditions are not encountered.
In particular, before conducting wireline operations, a great length of pressure-control pipe must always be installed, the length of the riser being dependent upon the length of the wireline suspended tools which must be accommodated within the long riser. Such long riser equipment is large, heavy, and requires considerable time to install, operate, and remove from the well after completion of wireline operations. Furthermore, the ram-type blowout preventers utilized beneath the long riser cannot be used to provide a seal about a moving wireline; however, they can be used to provide a seal about a wireline under static conditions. Consequently, the additional wireline stuffing box must be provided at the end of the riser to seal about moving wireline cables. Moreover, such ram-type blowout preventers, which are capable of allowing the through passage of wireline suspended tools, such as logging tools, are large, heavy, and bulky--thus presenting equipment handling problems at the wellhead.
Accordingly, prior to the development of the present method and apparatus, there has been no method or apparatus for conducting wireline operations in oil and gas wells under blowout conditions which: is efficient to install, operate, and remove; requires a minimum amount of equipment to be installed prior to performing wireline operations under normal conditions thereby greatly facilitating wireline operations on the large majority of wells for which blowout conditions are not encountered; provides a seal on a moving wireline; is economical; is safe in its operation; and does not require large, heavy, and bulky ram-type blowout preventers. Therefore, the invention provides a long sought efficient, safe, and less costly method and apparatus for conducting wireline operations in oil and gas wells, particularly uncased wells which may be subject to blowout, or other emergency, conditions.